// 添加背景图片
body {
  background: url(/images/background.webp),url(/images/background.jpeg); // 你给的背景图
  -moz-background-size:100% 100%;
  -webkit-background-size:100% 100%;
  top: 0;
  left: 0;
  z-index: -2;
  background-repeat: no-repeat;
  background-attachment: fixed;
  background-position: 50% 50%;
  background-size: cover;
}
